The invention relates to a boat hull having an aft portion which aids in allowing the boat to get on plane.
In a conventional "V" type hull, the bottom of the boat terminates at the transom. In boats of this nature, either an outboard motor can be set on the transom or a stern drive, which has a motor within the boat directly in front of the transom and with a propulsion leg sticking through the transom, can be used to power the boat. In these types of boats, the driving force or propeller is behind and below the rear most portion of the boat.
In other hull constructions, such as that shown in U.S. Pat. No. 4,361,102, the bottom of the central portions of the hull actually terminates forward of the transom so that there is a step between the bottom of the hull and the transom.
When boats of either of the above general type go from a rest or idle condition to a full speed planing condition, they must accelerate through a condition which is known as "getting on plane". When these boats are getting on plane, the angle of the boat in the water can be quite steep, which can hinder the visibility of the operator, as well as creating an inefficient running condition.
Depending on the weight of the boat, the position of the load in the boat, and the amount of power of the engine, the condition of getting on plane can last an extended length of time. Once on plane, the angle of attack of the boat with respect to the water will level off and visibility is restored to the operator.
In order to enhance the speed in which boats of the above type get on plane, it is known in the art to attach a pair of trim tabs to the transom of the boat. These trim tabs are generally made of metal and extend rearwardly from and pivot about an axis parallel to the bottom of the boat at the junction of the bottom of the boat and the transom. These trim tabs can be pivoted about this axis by means of a hydraulic cylinder having one end attached to their rearward edge and the other to the transom. As can be appreciated, these trim tabs stay in the water during all running conditions and create additional wetted surface area for the boat even after the boat has gotten onto plane which will tend to slow the boat's progress through the water once on plane.
U.S. Pat. No. 4,492,176 discloses a boat hull having outboard portions of the bottom of the hull which extend rearwardly of the transom. These portions are at the same level as the hull and thus are in the water and creating drag at all times, similar to the above described trim tabs.
U.S. Pat. No. 4,584,959 discloses a boat hull having after-sponsons which extend rearwardly from the transom of the boat along either side of the motor well. These sponsons have lower surfaces 46 which allegedly cause the boat to plane more quickly. However, the length and shapes of these surfaces are not clearly defined in this patent, but, as seen in at least FIG. 3 of the patent, they are not parallel to the bottom of the boat hull nor are they of constant width throughout their length. To the contrary, the overall shape of the sponson is described as aerodynamically streamlined in order to aid in the ability of the speed boat in this patent to move through the air. This requirement would teach away from the sponsons being parallel to the bottom of the main hull or having the same cross sections as the main hull throughout their length, as this is not an aerodynamically efficient shape.